The use of double grips in tool exchange systems enables tools to be exchanged in a single conveyance step between a tool room and the machining spindle. They clearly result in reduced tool exchange times compared to those of single grips since these must first deposit the old tool to the main spindle.
German patent publication 1 477 501 describes a tool exchanger for a machine tool with a horizontal spindle featuring two diametrically opposed tool grips which can be rotated 180.degree. so that the selection of a new tool from the tool room and the conveyance of the tool in a spindle-close standby position may take place during the machining time with the previous tool. A significant disadvantage of this embodiment lies in the fact that each tool grip must have its very own independent activation device, which results in a very expensive and bulky construction in connection with the large rotation angle.
German patent publication 30 17 613 describes another tool exchanger for machine tools with a spindle arranged along a rotating angle head, featuring a double gripping device arranged to rotate along a conveyance arm in order to serve one machining spindle or the other. The conveyance arm can be moved parallel to and perpendicularly to the spindle axis and can be rotated along another axis. The mechanisms which are required to operate the machining spindle in the various rotation positions of the angle head are technically complex and require significant space.